The present invention relates generally to fluid-filled chambers for use in the sole structure of an article of footwear.
Conventional articles of athletic footwear include two primary elements, an upper and a sole structure. The upper provides a covering for the foot that comfortably receives and securely positions the foot with respect to the sole structure. The sole structure is secured to a lower portion of the upper and is generally positioned between the foot and the ground. In addition to attenuating ground reaction forces (that is, providing cushioning) during walking, running, and other ambulatory activities, the sole structure may influence foot motions (for example, by resisting pronation), impart stability, and provide traction, for example. Accordingly, the upper and the sole structure operate cooperatively to provide a comfortable structure that is suited for a wide variety of athletic activities.
The upper is often formed from a plurality of material elements (for example, textiles, polymer sheets, foam layers, leather, synthetic leather) that are stitched or adhesively bonded together to define a void on the interior of the footwear for comfortably and securely receiving a foot. More particularly, the upper forms a structure that extends over instep and toe areas of the foot, along medial and lateral sides of the foot, and around a heel area of the foot. The upper may also incorporate a lacing system to adjust fit of the footwear, as well as permit entry and removal of the foot from the void within the upper. In addition, the upper may include a tongue that extends under the lacing system to enhance adjustability and comfort of the footwear, and the upper may incorporate a heel counter.
The sole structure generally incorporates multiple layers: a sockliner, a midsole, and a ground-engaging outer member. The sockliner is a thin, compressible member located within the upper and adjacent to a plantar (that is, lower) surface of the foot to enhance footwear comfort. The midsole is secured to a lower surface of the upper and forms a middle layer of the sole structure. Many midsole configurations are primarily formed from a resilient polymer foam material, such as polyurethane (PU) or ethyl vinyl acetate (EVA), that extends throughout the length and width of the footwear. The midsole may also incorporate plates, moderators, and/or other elements that further attenuate forces, influence the motions of the foot, and/or impart stability, for example. The ground-engaging outer member may be fashioned from a durable and wear-resistant material (for example, rubber) that includes texturing to improve traction.
Further, the sole structure may include fluid-filled chambers to provide cushioning and stability. Upon inflation, such chambers experience pressure that is evenly distributed to all portions of the inner surface of the bladder material from which the chamber is formed. Accordingly, the tendency is for chambers, when inflated, to take on an outwardly rounded shape. For use as cushioning members in footwear, however, it is desirable to provide the chambers with a relatively flat form, to serve as a platform for receiving the sole of a foot of a wearer. Thus, to limit the expansion of the top and bottom portions of the chamber upon inflation, sole structures have been developed with chambers having one or more tensile structures that link the top portion of the chamber to the bottom portion of the chamber in order to maintain the chambers in a substantially planar configuration. However, such tensile members may provide increased stiffness to the chambers. Accordingly, there is a need for chamber configurations that provide tensile member-equipped fluid-filled chambers with increased flexibility.